1. Field of the Invention
The present invention relates to the art of mechanical axle/suspension systems for vehicles. More particularly, the invention relates to the art of mechanical spring axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, which locate the vehicle axle(s) and stabilize the vehicle during vehicle operation. Still more particularly, the invention relates to a spring seat for a mechanical spring axle/suspension system that includes continuous window welds and enables the use of a thin-wall axle, thereby saving weight and cost.
2. Background Art
Heavy-duty vehicles that transport freight, for example, tractor-trailers or semi-trailers and straight trucks, include suspension assemblies that connect the axles of the vehicle to the frame of the vehicle. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience, reference herein will be made to a subframe, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle primary frames, movable subframes and non-movable subframes.
In the heavy-duty vehicle art, reference is often made to an axle/suspension system, which typically includes a pair of transversely-spaced suspension assemblies and the axle that the suspension assemblies connect to the vehicle subframe. The axle/suspension system of a heavy-duty vehicle acts to locate or fix the position of the axle and to stabilize the vehicle. More particularly, as the vehicle is traveling over-the-road, its wheels encounter road conditions that impart various forces to the axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. These forces consequently act to place or create loads on the axle and the suspension assemblies. In order to minimize the detrimental effect of these forces and resulting loads on the vehicle subframe and other vehicle components as the vehicle is operating, and in turn on any cargo and/or occupants being carried by the vehicle, the axle/suspension system is designed to absorb or dampen at least some of the forces and/or resulting loads.
Two common types of heavy-duty vehicles are known in the art as dry freight vans and refrigerated vans. Dry freight vans include enclosed trailers to keep their freight dry, and are used to transport a wide variety of non-perishable consumer and industrial goods. Refrigerated vans include enclosed trailers with refrigeration systems, and typically are used to transport perishable goods. Such dry freight vans and refrigerated vans have traditionally employed axle/suspension systems that utilize mechanical spring suspension assemblies. These mechanical spring suspension assemblies typically include a pair of leaf spring sets or stacks that are transversely spaced and are connected to the axle. The pair of leaf spring sets is typically connected to the axle utilizing U-bolt connection so as to not compromise the integrity of the springs. Each leaf spring stack is engineered to carry the rated vertical load of its respective axle. Ordinarily, a trailer of a dry freight or refrigerated van employs one or more mechanical spring axle/suspension systems at the rear of the trailer, that is, a front axle/suspension system and a rear axle/suspension system, which is a configuration that is collectively referred to in the art as a trailer tandem axle/suspension system. As is known to those skilled in the art, the front end of the trailer is supported by a separate axle/suspension system of the tractor. For the purpose of convenience, reference herein shall be made to a spring axle/suspension system, or a mechanical axle/suspension system, with the understanding that such reference is to a trailer tandem mechanical spring axle/suspension system.
It is understood that each one of the front and rear spring axle/suspension systems includes a generally identical pair of transversely-spaced, longitudinally-extending leaf spring sets or stacks, each one of which is disposed on a respective one of the driver's side and passenger side of the vehicle. Inasmuch as each leaf spring set of each front and rear spring axle/suspension system is generally identical to the other, only one of each of the front and rear leaf spring sets will be described herein. In the prior art, spring axle/suspension systems have utilized a clamp assembly to connect each leaf spring set to the axle.
More particularly, the clamp assembly includes a top block that is disposed on the upper surface of the leaf spring, a top axle seat that extends between the bottom of the leaf spring and the upper portion of the axle in alignment with the top block, and a bottom axle seat, which is a curved plate disposed on the lower portion of the axle in alignment with the top block and the top axle seat. The clamp assembly also includes a pair of U-bolts, each one of which engages top block and extends through a pair of openings formed in bottom axle seat. In this manner, top block, leaf spring, top axle seat, axle, and the bottom axle seat are rigidly clamped together when nuts are tightened onto the ends of the U-bolts.
The top axle seat and the bottom axle seat each are rigidly connected to the axle near its outboard end utilizing line welds. A line weld is a weld that begins at one point and ends at a separate point. The starting point of the line weld and the end point of the line weld create an area that is susceptible to stress, known as stress risers. As a result, the starting point and end point of the line weld include undesirable areas of stress risers. Thus, when a component is line welded to a hollow axle central tube, an area on the axle wall adjacent each weld endpoint is created that is generally more susceptible to stress than a non-welded area, or to areas that employ other types of welds.
As a result, when forces and resulting loads act upon the axle, a line welded area along the axle central tube is generally more susceptible to failure from such forces and/or loads than a non-welded area. In order to compensate for the increased susceptibility to stress that is caused by line welds, the wall thickness of the axle typically is increased, which undesirably increases the amount of material used to manufacture the axle, and also undesirably increases the weight of the axle.
As a result, a need has existed in the art for a spring axle/suspension system that overcomes the disadvantages of prior art systems by reducing stress risers associated with line welding a spring seat to the axle, thereby enabling the use of a thin-wall axle and reducing the weight and cost of the system. The mechanical axle/suspension spring seat for thin-wall axles of the present invention satisfies this need.